WASHINGTON — An international airborne telescope the White House proposed mothballing March 4 was squeezed out of NASA’s budget by other ongoing missions, in particular the flagship-class Cassini probe that has been orbiting Saturn since 2004, a senior agency official said.

The White House proposed grounding the billion-dollar Stratospheric Observatory for Infrared Astronomy (SOFIA) in part to avoid forcing the 16-year-old Cassini orbiter to compete with the 1.5-year-old Mars Curiosity rover for extended mission funding, according to budget documents. Cassini needs about $60 million a year to reach its currently targeted mission conclusion in September 2017.

SOFIA, which is finally on the cusp of full-scale science operations after nearly two decades of development, could still be saved if NASA’s partner on the project, the German Aerospace Center (DLR), ponies up the roughly $85 million a year needed to keep the observatory flying. Otherwise, SOFIA heads to the hangar after the current fiscal year ends Sept. 30, a NASA official said in a conference call with the press March 4.

“SOFIA does have a rather large operating cost, compared to other missions,” NASA Chief Financial Officer Elizabeth Robinson said on the call. That forced NASA to make tough trades “about how many [missions] you keep going, and how much [funding] you free up.”

An astrophysics observatory designed for 20 years of science operations, SOFIA pairs a heavily modified Boeing 747SP aircraft — a variant last delivered to a commercial customer in 1989 — with a 2.5-meter telescope that takes images in spectra ranging from the visible to the far-infrared. The aircraft was designed to host a variety of instruments, which could be swapped in and out, depending on the kind of observations astronomers wanted to make.

NASA put German officials on notice about the proposed SOFIA cancellation late the week of Feb. 28, Robinson said. The U.S. agency is leaving it to Germany, and any other bill-payers it can find, to cover NASA’s share of SOFIA operating costs. 

SOFIA cost about $1.1 billion, in 2000 dollars, to build, according to a Government Accountability Office report released in 2013. The observatory’s planned 20-year mission would have brought its total cost to about $3 billion, according to the report. 

NASA and DLR divided SOFIA’s development and operating expenses on a roughly four-to-one basis, Paul Hertz, NASA’s director of astrophysics, said during the conference call.

As is the case with most of NASA’s international collaborations, DLR’s contribution to SOFIA is provided on an “in kind” basis. German scientists control 20 percent of SOFIA’s yearly research hours in exchange for the “personnel, parts and materials” DLR provided for the mission’s construction and operation, DLR spokesman Andreas Schütz said in a March 7 email.

DLR has spent roughly $140 million on SOFIA since 1996 “for the development of the telescope and the contribution to SOFIA’s operation,” Schütz said. DLR wants to continue SOFIA, but cannot afford to do so alone. To that end the agency “is working closely together with its partner NASA to find a solution to continue the flying Infrared Observatory,” Schütz said.

SOFIA has logged about 400 flight hours in a demonstration mode, according to Hertz.

Just one day before the conference call, John Grunsfeld, associate administrator for NASA’s Science Mission Directorate, told members of the National Research Council here that NASA was “going through the paperwork process to declare SOFIA fully operational.”

That process will still be completed, Hertz said, and SOFIA will fly for the remainder of the U.S. government’s 2014 budget year.

Even as the White House was preparing to announce the project’s cancellation the week of March 3, SOFIA was testing out one of the modular instruments provided by DLR, the Field Imaging Far Infrared Line Spectrometer. More test flights are on the slate, and the instrument was scheduled this April to start mapping regions of space where new stars are forming, Schütz said. 

SOFIA is operated for NASA by the Universities Space Research Association of Columbia, Md., and flies out of NASA’s Armstrong Flight Research Center (formerly Dryden) in Edwards, Calif. 

Even if SOFIA is retired this fall, astronomers will have a few near-term options for observing the heavens in the wavelengths SOFIA covered, Hertz said.

“Sofia covers a very broad range of wavelengths, from the visible all the way out to the submillimeter,” he said. The Spitzer Space Telescope and planned James Webb Space Telescope monitor the shorter wavelengths covered by SOFIA, he said.

In addition, the Atacama Large Millimeter/submillimeter Array, a ground-based observatory located about 5 kilometers above sea level on the Chajnantor plateau in central Chile, is sensitive to some of the longest wavelengths in SOFIA’s range, Hertz said.

However, SOFIA’s grounding would leave certain wavelengths, primarily those at or near the middle of the telescope’s range, unmonitored. “There aren’t any planned observatories that would fill that in,” Hertz said.

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NASA Budget Would Begin Work on New Science Missions, Ground SOFIA

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...